Symmetric Latching

A mode where a device’s source address/ports for the RTP/RTCP it sends to the Oracle Communications Session Border Controller (OCSBC) that are latched, are then used for the destination of RTP/RTCP sent to the device.

After allocating the media session in SIP, the OCSBC sets the restriction mode and the restriction mask for the calling side as well as for the called side. It sets the source address and address prefix bits in the flow. It also parses and loads the source flow address into the MIBOCO messages. After receiving the calling SDP, the OCSBC sets the source address (address and address prefix) in the appropriate flow (the flow going from calling side to the called side). After receiving the SDP from the called side, the OCSBC sets the source address in the flow going from the called side to the calling side.

The OCSBC uses either the address provided in the SDP or the layer 3 signaling address for latching. You also configure the OCSBC to enable latching so that when it receives the source flow address, it sets the address and prefix in the NAT flow. When the NAT entry is installed, all the values are set correctly. In addition, sipd sends the information for both the incoming and outgoing flows. After receiving SDP from the called side sipd, the OCSBC sends information for both flows to the MBCD so that the correct NAT entries are installed.

Enabling restricted latching may make the OCSBC wait for a SIP/SDP response before latching, if the answerer is in a restricted latching realm. This is necessary because the OCSBC does not usually know what to restrict latching to until the media endpoint is reached. The only exception could be when the endpoint’s contact/IP is cached.